HR: 16:25h
AN: H54E-02 [Abstracts]
TI: A fine-scale turbidity record as a view of fine bed sediment supply, transport, and dynamics
AU: * Leonardson, R
EM: rebeccal@ce.berkeley.edu
AF: University of California, Berkeley,
Civil and Environmental Engineering, 760 Davis Hall, Berkeley, CA 94720-1710, United States
AU: Hunt, J R
EM: hunt@ce.berkeley.edu
AF: University of California, Berkeley,
Civil and Environmental Engineering, 760 Davis Hall, Berkeley, CA 94720-1710, United States
AU: Dietrich, W E
EM: bill@eps.berkeley.edu
AF: University of California, Berkeley,
Earth and Planetary Science, 313 McCone Hall, Berkeley, CA 94720-4767, United States
AB:
Fine bed sediments in gravel-bedded rivers are detrimental for salmonid reproduction, ecosystem productivity,
groundwater-surface water exchange, and streambank pumping operations. However, the quantity and grain size
of fine bed sediments are generally unknown. Direct measurements are temporally and spatially sparse, valid
for only a short length of time, and often lack volumetric, subsurface, and sediment quality analyses. California's
Russian River is impaired for both turbidity and sedimentation of the bed by fines. Bed sedimentation has been
relatively unquantified; we hypothesize that it is possible to extract information about the quantity and grain size of
bed sediment from the extensive record of streamflow and turbidity data available in the basin. A unique database
has been assembled by joining all US Geological Survey (USGS) daily and 15-minute monitoring data from the
basin (22,000,000 data points) with USGS water quality field-sampling data, NOAA atmospheric data, and
ancillary data collected by the USGS, the California Department of Fish and Game, the Sonoma and Mendocino
County Water Agencies, and academic and private researchers. This database has been organized with a data
cube, which allows for quick retrieval of information organized by different dimensions (e.g. by water year,
frequency, site, etc.) Analyses made thus far have focused on six years of 15-minute turbidity and streamflow
data collected at two gauging stations (drainage areas 900 and 3500 km2) on the main stem. Differences in the
relationship between turbidity and suspended sediment concentration during different flow phases and the
progression of turbidity/streamflow hysteresis loops over series of storms suggest that early in the initial rising
limb, turbidity is largely controlled by local mobilization of fines in the bed. Farther into the discharge event, fine
material loads are interpreted to become source-dependent (i.e. sediment mobilized from well upstream.) To
build on our analysis, we have created additional databases of individual storms and turbidity spikes. The
database/data cube structure permits both expansion of the study (e.g. into long-term trends of sediment storage
and flux by inclusion of lower-frequency data collected since the 1960's), and sharper focus on the question of
bed sediment (through incorporation of short, high-frequency turbidity datasets at additional sites and estimation
of bed shear stress from ancillary data.) In general, a data cube built with high frequency flow and turbidity data
from multiple years and gauging stations provides unique opportunities for testing models for fine sediment
dynamics in gravel-bedded streams.
DE: 1825 Geomorphology: fluvial (1625)
DE: 1861 Sedimentation (4863)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting